Electrical isolation of x-ray semiconductor imager pixels

ABSTRACT

To mitigate the influence of charge sharing occurring in semiconductor detectors, an improved semiconductor detector ( 200 ) is provided, which comprises: a plurality of anodes ( 210 ) arranged to form at least one opening ( 230 ), each opening being formed by two anodes in the plurality of anodes; at least one cathode ( 220 ); a detector cell ( 240 ) located between the plurality of anodes and the at least one cathode; wherein the detector cell comprises at least one groove ( 250 ), each of the at least one groove having a first opening ( 252 ) aligned with one of the at least one opening being formed by two anodes in the plurality of anodes, each of the at least one groove extending towards the at least one cathode. By forming grooves in the detector cell, the charge cloud generated by a single photon can be received by a corresponding anode instead of several neighboring anodes, which thereby improves the spectral resolution and count rate of a semiconductor detector.

FIELD OF THE INVENTION

The present invention relates to a semiconductor detector, particularlyto a medical semiconductor detector.

BACKGROUND OF THE INVENTION

In medical industry, direct conversion materials, such as Si, GaAs,CdTe, and CZT gain more and more importance in modalities, such as CTdetectors, X-ray detectors, Gamma detectors, and nuclear medicine inwhich the scintillator type detectors are still state of the art. Theiradvantage over scintillators is the possibility of photon-countingcoupled with a good energy solution. However, these direct conversionmaterials are vulnerable because of charge sharing, a phenomenon inwhich the charge cloud generated by a single photon is collected byseveral neighboring electrodes. FIG. 1 shows that a charge cloudgenerated by one photon is collected by three neighboring electrodes.The phenomenon of charge sharing disturbs the spectral resolution andcount rate performance of detectors. In high-rate detectors, thephenomenon of charge sharing limits the effort of adopting smallerpixels. At the same time, the phenomenon of K-escape also limits theadoption of smaller pixel sizes. K-escape is primarily caused by partialtransport of the primary energy, e.g. X-ray energy, through anotherquantum, e.g. an X-ray quantum, to a neighboring pixel.

Thus there is a need to solve or mitigate the negative influence ofcharge sharing, especially in detectors based on direct conversionmaterials.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedsemiconductor detector.

In one embodiment, it is advantageous to mitigate the negative effectcaused by charge sharing and thereby improve the spectral resolution andcount rate performance of semiconductor detectors.

In one embodiment, it is advantageous to mitigate, or even eliminate theK-escape phenomenon of semiconductor detectors and thereby improve thecount rate performance of semiconductor detectors.

In one embodiment, it is advantageous to mitigate the negative effect ofcharge sharing and K-escape on the miniaturization of pixel sizes ofsemiconductor detectors.

In a first aspect, according to one embodiment of the invention, asemiconductor detector is provided, comprising: a plurality of anodesarranged to form at least one opening, each opening being formed by twoanodes in the plurality of anodes; at least one cathode; a detector celllocated between the plurality of anodes and the at least one cathode;wherein the detector cell comprises at least one groove, each of the atleast one groove having a first opening aligned with one of the at leastone opening being formed by two anodes in the plurality of anodes, eachof the at least one groove extending towards the at least one cathode.Forming one or more grooves in the detector cell is efficient to guidethe charge cloud generated by a single photon received by acorresponding anode, instead of being received by several neighboringanodes. This provides the advantage of mitigating the negative effect ofcharge sharing on spectral resolution and count rate performance.

In a further embodiment, each groove extends along a directionperpendicular to the plane of its first opening. In other words, eachgroove is perpendicular to the tangential plane of a correspondingopening formed by two corresponding adjacent anodes. It is easy tomanufacture this shape of groove.

In another embodiment, each groove extends along a direction away from adirection which is perpendicular to the plane of its first opening. Inother words, the direction of extension of the groove is inclinedinstead of being perpendicular to the tangential plane of acorresponding opening formed by two corresponding adjacent anodes. Thisshape is advantageous in that it decreases the phenomenon of reducingDQE (Detector Quantum Efficiency) of detectors.

In a second aspect, according to one embodiment of the invention, eachgroove comprises an insulator which is helpful in mitigating, or eveneliminating, the negative effect of the K-escape phenomenon. It ispreferred to use insulator with a high atomic number Z.

These and other aspects, features and/or advantages of the invention areapparent from and will be elucidated with reference to the embodimentsdescribed hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the phenomenon of charge sharing;

FIG. 2 illustrates a semiconductor detector comprising groovesperpendicular to the surface of a plurality of anodes, according to oneembodiment of the invention;

FIG. 3 illustrates a semiconductor detector comprising grooves extendingalong a tilt angle away from the perpendicular direction of a pluralityof anodes, according to one embodiment of the invention;

FIG. 4 illustrates a semiconductor detector comprising grooves filled byinsulators, according to one embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of a structured semiconductor detector which mitigates orovercomes the drawback of the charge sharing effect in currentsemiconductor detectors is shown in FIG. 2. The detector 200 comprises aplurality of anodes 210, at least one cathode 220, and a detector cell240. The anodes and the at least one cathode can be arranged inparallel, or in another configuration. Every two adjacent anodes form anopening 230. From each opening, a groove 250 extends into the detectorcell 240, with its direction perpendicular to the plane of the opening230. Each groove 250 has a first opening 252, which may have the samewidth as the corresponding opening 230, or which may be larger/smallerthan the corresponding opening 230. It can clearly be seen that, due tothe existence of grooves, a charge cloud generated by a photon isreceived by one corresponding anode instead of by two or more adjacentanodes.

Another embodiment is shown in FIG. 3, in which the direction ofextension of the grooves is not perpendicular to the plane of theopening 230, i.e. the plane of the first opening 252′ of each groove.Each groove 250′, or at least part of the grooves, extends along a tiltdirection which is not perpendicular to the opening 230, i.e. its firstopening 252′. The drawback of a reduced DQE (Detector QuantumEfficiency) caused by a reduced stopping power can be mitigated with thetilt direction. The angle of the extending direction of the grooves 250′may vary in dependence on some factors, including mechanical stability,stopping power, density and thickness of the sensor material, and alsothe X-ray spectrum used. The skilled person can adapt the angle of theextending direction to the real situation. Optionally, the thickness ofthe detector cell 240, e.g. the crystal used, can be slightly increased.

In the embodiments of FIG. 2 and FIG. 3, the depth of grooves may varyin dependence on demands and/or manufacturing techniques. The groovesmay extend slightly into the detector cell 240, halfway into thedetector cell 240, or even extend from the opening 230 to the plane ofthe cathode. In the latter case, the groove has a second opening locatedat the surface of the cathode.

The embodiments shown in FIG. 2 and FIG. 3 can be combined in anyconfiguration. For example, it is allowed to combine part of the groovesextending along a direction perpendicular to the plane of their firstopening 252 and part of the grooves extending along tilt directions awayfrom the perpendicular direction of the plane of their first opening252, respectively. Especially for the part of the detector cell which israther blind to the incoming photons, e.g. X-ray photons, the groovesextend along the perpendicular direction. For the other part of thedetector cell, the grooves extend along tilt directions, which isadvantageous for improving the DQE.

K-escape is caused by a photo-effect releasing a K-shell electron froman atom in the detector cell, with the K-shell being refilled almostinstantly from a higher shell electron and thereby releasing acharacteristic amount of energy in the form of a K-escape photon. Thisphoton can be transported from one place to another in the detector celland may give rise to another signal elsewhere in the detector. FIG. 4illustrates an embodiment according to the present invention, whichmitigates/eliminates the K-escape phenomenon. Each groove 250″ is filledwith an insulator which can effectively stop this migrating energy, i.e.K-escape photons, denoted by reference numeral 260, and can thussuppress or even prevent the production of disturbing signals.Optionally, the insulator is made of an insulating material with a highatomic number Z.

The embodiments of the semiconductor detector shown in FIGS. 2 to 4 canbe used in medical equipment, at least including CT scanners, X-raydetectors and Gamma-ray detectors.

The embodiments shown in FIGS. 2 to 4 can be combined in anyconfiguration. Although the present invention has been described withreference to the specified embodiments, it is not intended to be limitedto the specific form set forth herein. Rather, the scope of the presentinvention is limited only by the accompanying claims. In the claims, useof the verb “comprise” and its conjugations does not exclude thepresence of other elements or steps. Although individual features may beincluded in different claims, these may possibly be combinedadvantageously, and the inclusion in different claims does not implythat a combination of features is not feasible and/or advantageous. Inaddition, singular references do not exclude a plurality. Furthermore,reference signs in the claims shall not be construed as limiting thescope.

1. A semiconductor detector comprising: a plurality of anodes arranged to form at least one opening, each opening being formed by two anodes in the plurality of anodes; at least one cathode; a detector cell located between the plurality of anodes and the at least one cathode; wherein the detector cell comprises at least one groove, each of the at least one groove having a first opening aligned with one of the at least one opening being formed by two anodes in the plurality of anodes, each of the at least one groove extending towards the at least one cathode.
 2. The semiconductor detector according to claim 1, wherein each of the at least one groove extends along a direction perpendicular to the plane of its first opening.
 3. The semiconductor detector according to claim 1, wherein each of the at least one groove extends along a direction not perpendicular to the plane of its first opening.
 4. The semiconductor detector according to claim 2, wherein each of the at least one groove has a second opening aligned with a surface of the at least one cathode.
 5. The semiconductor detector according to claim 1, wherein each of the at least one groove comprises an insulator.
 6. The semiconductor detector according to claim 5, wherein the insulator is made of a material having a high atomic number Z.
 7. The semiconductor detector according to claim 1, wherein the detector cell is made of a direct conversion material.
 8. The semiconductor detector according to claim 1, further configured to detect x-ray quanta.
 9. A medical scanner comprising a semiconductor detector, wherein the semiconductor detector comprises: a plurality of anodes arranged to form at least one opening, each opening being formed by two anodes in the plurality of anodes; at least one cathode; a detector cell located between the plurality of anodes and the at least one cathode; wherein the detector cell comprises at least one groove, each of the at least one groove having a first opening aligned with one of the at least one opening being formed by two anodes in the plurality of anodes, each of the at least one groove extending towards the at least one cathode.
 10. A medical scanner according to claim 9, being any one of a CT scanner, an X-ray detector, and a Gamma-ray detector. 